Impact of COVID-19 on football attacking players’ match technical performance: a longitudinal study

This study examined the impact of COVID-19 on 28 indicators of match technical performance (MTP) for football attacking players upon their return to play. Analyzing data from 100 players in the Big Five European football leagues, covering 1500 matches each before and after COVID-19 over 3 years (2020–2023), revealed significant differences in 76% of players’ MTP indicators. Notably, 14 indicators, particularly the five indicators linked to scoring, significantly decreased post-COVID-19. On average, players needed 3.09 matches to regain pre-infection MTP levels. The impact varied across player groups, with those in the elite group showing a milder effect; they required an average of 2.64 matches for recovery, compared to the control group’s 3.55 matches. We found that, with increasing age, the majority of players’ MTP indicators did not exhibit significant changes, both before and after they contracted COVID-19. In conclusion, the study highlighted the negative impact of COVID-19 on football attacking players’ MTP. Players in the elite group experienced fewer adverse effects than those in the control group. This insight assisted coaches and managers in evaluating the impact of COVID-19 and similar virus-induced illnesses on players’ MTP, enabling them to formulate training regimens for recovery and specific match tactics upon players' return to play.


Player selection
Our study concentrates on players from the Big Five leagues, renowned for their global prestige and ability to attract world-class talent, as they represent the pinnacle of football competition 68,69 .We specifically target attacking players, identified as forwards in the Premier League, La Liga, and Ligue 1, and as strikers in the Bundesliga and Serie A, per the leagues' official websites.
To conduct a secondary verification of players' positions through third-party channels and to accomplish the task of selecting elite players, we rely on FIFA 23 player ratings, a credible source from the widely recognized football simulation video game licensed by FIFA, covering the period from 1993 to 2023.This game includes over 19,000 players, more than 700 teams, and 30 global events 70 , providing a rich dataset invaluable for coaches and sports analysis 71,72 .The use of this video game data for analytical purposes, including predicting match outcomes and evaluating player wages with machine learning, has become increasingly popular since 2014 73,74 .For example, researchers have utilized it in machine learning projects to accurately predict match results 75 and determine if a player's wage is above or below the median based on age and overall attributes 76 .For our analysis, attackers within the top 50 FIFA 23 overall ratings from the Big Five were selected as the elite group.Should any selected player lack confirmed COVID-19 infection data, the next highest-rated attacker serves as a substitute.Conversely, attackers from the Big Five in the bottom 50 of the ratings constitute the control group, with substitution criteria applied equivalently.Ultimately, the distribution of the 100 attacking players across the Big Five is presented in Table 1, closely aligned with the UEFA association rankings.
In the elite group, Messi boasts the highest rating (91), while Giroud holds the lowest (82), resulting in an average of 84.76.In contrast, within the Control Group, the average score stands at 76.48, with Ruben Garcia securing the highest at 79 and Sulaimana attaining the lowest at 75.A statistically significant difference exists between the two player groups concerning overall ratings (p < 0.001) but not in relation to other indicators (Fig. 1).

Indicator selection
The study uses 28 MTP indicators for attacking players, as defined in Table 2.

Study design
A series of independent t-tests were conducted to evaluate whether attacking players, post-COVID-19 infection, demonstrated a decline in diverse MTP indicators upon their return to the field compared to their individual pre-COVID-19 MTP data.This methodology was similarly applied to investigate potential distinctions in the negative impact on MTP indicators between the elite and control groups, both having experienced COVID-19 infection.
To assess the recovery progress of attacking players post-COVID-19 contraction, we calculated the average values of each MTP indicator for the 15 matches preceding their infection.Subsequently, we compared these averages with the respective data from matches played by the players upon their return.If, in the Xth match, a player's performance in a specific MTP indicator equaled or surpassed their pre-COVID-19 average for that indicator, it was deemed that the player had reached their pre-COVID-19 level in that particular aspect after X matches.This straightforward assessment method facilitated the evaluation of recovery time for players who had experienced COVID-19 and subsequently resumed playing.In testing the hypothesis concerning age, linear regression analyses are conducted with age as the independent variable and MTP indicators such as xG as the dependent variable.The objective was to investigate the association between age and the indicators and determine whether older attacking players needed more matches to regain their pre-COVID-19 levels.
According to Hayes, the effect of X on some variable Y is moderated by W if its size, sign, or strength depends on or can be predicted by W. In that case, W is said to be a moderator of X's effect on Y 77 .In this study, X represents the age of the players at the time of COVID-19 infection.W signifies the pre-or post-COVID-19 status, presented as a binary variable with W = 1 denoting pre-COVID-19 and W = 2 indicating post-COVID-19.The MTP indicators mentioned earlier serve as Y.When a specific MTP indicator is considered Y, the remaining indicators act as control variables, and so forth.This methodology aims to explore whether the impact of player age on each MTP indicator is influenced by COVID-19 infection status.

76% of players showed differences in MTP indicators after COVID-19 infection
As illustrated in Fig. 2, players in both the elite (left) and control (right) groups exhibited numerous indicators that were significantly different before and after contracting COVID-19.We observed that 76% of the 100 attacking players who contracted COVID-19 displayed significant differences in at least one MTP indicator compared to their pre-COVID-19 levels upon returning to the match.Among them, 92% of the elite group players met the criteria, while only 85% of the control group players did.On average, each player had 3.2 MTP indicators showing significant differences after contracting COVID-19.The elite group had an average of 3.4 indicators, while the control group had an average of 3 indicators.
The Touches and Touches Live indicators, each with twenty cases, exhibited the most notable changes following COVID-19 infection, as depicted in Fig. 3.In contrast, Def Pen and GCA had only four cases each and demonstrated the least significant differences.Def Pen had the fewest cases in the elite group, with just one, but MedAtt displayed the most, with twelve cases of significant differences.Within the control group, DriSucc% and www.nature.com/scientificreports/DriDis had the fewest occurrences-just two each-while Touches and Touches Live had the most significant differences-nine appearances.

The performance of attacking players was weakened by COVID-19, with the elite group being less affected than the control group
Independent-samples t test was conducted on the MTP indicators of players before and after COVID-19 infection, revealing that the p values of fourteen MTP indicators, including xG and npxG, were less than 0.05, indicating significant differences.The mean values of the aforementioned MTP indicators before COVID-19 infection were all higher than those after COVID-19 infection (Table 3).From the table, we observed significant decreases in xG, npxG, xAG, SCA, and GCA, which are all scoring-related indicators, for attacking players after contracting COVID-19.In the passing category, only LongCmp, involving long passes, showed a significant decrease in attacking players after COVID-19 infection compared to before.Regarding the possession category, the number of touches by attacking players in Mid 3rd, Att 3rd, and Att Pen significantly decreased after COVID-19 infection, particularly in Att 3rd, where the number of touches decreased by 1.057 times per game compared to pre-COVID-19.In the take-ons subcategory, the DriAtt and DriSucc also showed significant declines.After www.nature.com/scientificreports/COVID-19 infection, attacking players received 1.527 fewer passes per game compared to pre-COVID-19.These results partially support hypothesis H1a.Independent-samples t test was conducted to compare the MTP indicators of the elite group and the control group before and after contracting COVID-19 (Table 4).The results showed that thirteen indicators in the control group exhibited significant differences (p < 0.05) before and after infection, while only seven indicators in the elite group showed significant differences.Among the same six indicators significantly affected after contracting COVID-19 in both group, the control group demonstrated a greater decrease in xG, Att Pen, and DriSucc% compared to their counterparts in the elite group.On the other hand, indicators such as npxG, xAG, and SCA showed a smaller negative impact on the control group after contracting COVID-19 than on the elite group.
The control group's players were more impacted in the possession category, particularly in Touches, Take-ons, and Receiving.Notably, the control group's attackers had 2.536 fewer touches per game, 1.465 fewer receptions per game in Att 3rd, and 1.727 fewer receptions per game in ReceivingRec after contracting COVID-19.In contrast, the elite group's attackers exhibited a significant decline in long-passing ability, with a 4.491% reduction in success rate.
Additionally, certain indicators exhibited marginal significance differences (0.1 > p > 0.05), such as DriSucc% in the elite group and GCA, ShortCmp, Def 3rd, Mid 3rd and DriMis in the control group.While the elite group's success rate in dribbling marginally decreased after COVID-19 infection, the 3.785% reduction per game was considerably lower than the control group's 5.058% reduction.These findings supported Hypothesis H1b.

Average 3.09 matches for MTP of attacking players to recover to pre-COVID-19 levels; the elite group recovers more quickly than the control group
Figure 4 reveals that several indicators experienced a notable decline in players' first match after COVID-19 infection but gradually improved in subsequent matches.On average, it took 3.09 matches for the MTP indicators of 100 attacking players to return to their pre-COVID-19 levels.The indicators in the scoring, passing, and possession categories required 3.65, 2.88, and 3.03 matches to recover to the level before the players contracted COVID-19, respectively.Among them, ShortCmp% needed the fewest matches at 1.83, while GCA required the most matches at 4.21.The control group players, on average, needed 3.55 matches to recover their MTP indicators to pre-COVID-19 levels, which was higher than the elite group's average of 2.64 matches (Fig. 5).The most substantial difference was observed in GCA, where the elite group needed 2.78 matches compared to the control group's 5.64

Age did not have a significant influence on the recovery of MTP for attacking players
We conducted linear regression analysis using age as the independent variable and xG, npxG, and other MTP indicators as dependent variables to investigate whether the number of matches needed for attacking players to return to their pre-COVID-19 performance level significantly increased with age.No indicator supported this hypothesis in the study.This remained consistent when separately testing the elite and control groups.Consequently, attacking players recovering from COVID-19 and returning to matches do not experience a significant slowdown in the recovery of various MTP indicators due to older age.Hypotheses H3a and H3b were not supported.

Limited impact of age on changes in MTP indicators for attacking players after contracting COVID-19
We hypothesize that the players' MTP may decrease with age.Furthermore, we conjecture that after contracting COVID-19, the extent to which players' MTP decreases due to aging is greater than the extent before contracting COVID-19.

Discussion
In a football match, what directly impacts match results are actions involving the ball, including possession, passing, and shooting 78 .These collectively constitute a player's MTP.
In practice, distinguishing whether the COVID-19 virus itself directly affects a player's MTP or if it is the prolonged period without systematic training and matches after contracting COVID-19 that induces changes in a player's MTP can be challenging.Researchers find that longer mid-season may negatively affect momentum and performance 55 .The emergence of the COVID-19 pandemic has exacerbated this situation.However, for this study, we do not need to make this differentiation.We treat these aspects as a comprehensive and inseparable factual scenario.Our primary focus lies in assessing whether significant differences exist in various MTP indicators between players who have resumed play after contracting COVID-19 and their corresponding indicators before infection.
Notably, a substantial majority of players who contracted the virus, amounting to 76%, demonstrated significant alterations in at least one MTP indicator upon their return to matches.After returning to the field, attacking players recovering from COVID-19 exhibited notable differences in fourteen MTP indicators, including xG and npxG, in comparison to their pre-COVID-19 levels.These indicators fall within the scoring, passing, and possession categories.Our study reveals a significant decrease in all five scoring-related MTP indicators (xG, npxG, xAG, SCA, and GCA) among attacking players post-COVID-19 infection.This indicates a clear negative impact on attacking players post-COVID-19, given that scoring goals and assisting teammates is their primary match task 79,80 .
In the possession category, players exhibited the most indicators with significant decreases in matches post-COVID-19.Furthermore, players also experienced a decrease in receiving subcategories.This phenomenon can be interpreted from multiple perspectives.From a team-wide viewpoint, the reduction in team training due to COVID-19 restrictions left players tactically underprepared.The lack of training time and collective tactical work may have led teams to play a more compact game to avoid potentially costly mistakes 81 .From an individual player's perspective, these findings suggest that attacking players exhibit a reduced desire or ability to attack in the initial 15 matches after COVID-19 recovery.This decline in attacking desire or ability may stem from the impact of COVID-19 on their physical function and the absence of systematic training and matches, leading to their physical fitness not fully returning to optimal levels.Studies find that players may face challenges in positioning themselves correctly and executing appropriate movements due to compromised physical performance (e.g., endurance and speed), resulting in difficulties in carrying out their attacking tasks 47,48 .
In our study, six out of seven indicators in the elite group coincide with the indicators exhibiting a substantial decline in the control group after resuming play post-COVID-19 infection.Furthermore, the control group has seven additional indicators where the elite group did not show a notable decline upon returning to matches.This observation emphasizes that, although the control group has a lower average number of indicators displaying  www.nature.com/scientificreports/significant differences after contracting COVID-19 compared to the elite group, the absolute count of affected indicators remains relatively high, nearly doubling that of the elite group.This finding is similar to observations in other sports, where a wide range of examples suggests that several athletic performance indices, such as acceleration, endurance, or reaction rate, do not decline, despite previous reports of adverse effects of SARS-CoV-2 infections on maximal aerobic capacity and the nervous system in populations of nonelite athletes 82,83 .This could be related to top players having better physical conditions 84 and usually being under strict medical control 85 .Numerous studies support the notion that players tend to experience a decline in skill performance when they have poor physical fitness or undergo significant physical exhaustion, such as in the second half of a match 54,86,87 .The substantial reduction in the number of attempted long passes by players after COVID-19 recovery further corroborates this perspective.Executing long passes imposes greater demands on players' leg strength and other physical fitness aspects compared to short and medium-range passes.This aligns with previous research indicating a decrease in physical fitness indicators among players from La Liga, Serie A, Croatian HNL, and Polish Ekstraklasa after contracting COVID-19 37 .
For the same indicators significantly affected after contracting COVID-19 in both groups, the control group exhibited a more substantial decrease in xG, Att Pen, and DriSucc% compared to the elite group.Conversely, the indicators npxG, xAG, and SCA, which all fall within the scoring category, showed a less pronounced decrease in the control group after COVID-19 infection compared to the elite group.However, upon comparing the mean values of these indicators between the two groups, it was evident that the control group's attackers had significantly lower data than the elite group both before and after contracting COVID-19.We posit that the control group's attackers having inherently lower MTP data contributed to the limited reduction in their MTP data even after contracting COVID-19.Consequently, their reduction in the mentioned MTP indicators after contracting COVID-19 was smaller than that of the elite group.This observation is consistent with the notion that top players bear the primary responsibility for scoring within their teams 80 .
In the control group, indicators significantly affected after contracting COVID-19 were primarily concentrated in the possession category, specifically in the subcategories of Touches, Take-ons, and Receiving.This implies that the technical skills of the control group players suffered more adverse effects after contracting COVID-19 compared to the elite group.Although the elite group's success rate in dribbling exhibited a marginally significant decrease after contracting COVID-19 compared to before, the decrease of 3.79% per match was considerably lower than the control group's decrease of 5.06% per match.This discovery once again confirms that, in practical terms of matches, the negative impact on elite players is smaller than that on nonelite athletes 82,83 .
Shots on target appeared as a strong indicator to be considered and maximized by football teams, being more relevant than ball possession and passing for success 78 .Considering that scoring is the primary task for an attacking player, followed by possession and passing 79 , the difficulty of completing these tasks should also follow that order.This is because, in matches, defenders of opponents are likely to prioritize limiting the scoring ability of attacking players, followed by their possession and passing abilities 88 .The recovery speed of MTP-related indicators in matches after players contracted COVID-19 supports this perspective.On average, the MTP indicators for scoring, possession, and passing require 3.65 matches, 3.03 matches, and 2.88 matches, respectively, to return to the pre-COVID-19 level.Among all the indicators, ShortCmp% requires only 1.83 matches, while GCA requires the most, with 4.21 matches.The recovery of players' short passing ability is the quickest, which is related to players opting to play a more compact game to avoid potentially costly mistakes after returning to the field 81 .It may also be related to player behavior being influenced by tactical demands and/or conscious or unconscious self-protection 11 .After all, short passing is one of the most fundamental techniques in football and one of the safest to perform 89 .Conversely, GCA, which represents a player's offensive actions directly leading to a goal, such as passes, take-ons, and drawing fouls, is a core indicator in the scoring category 90 .It demands much more from players than short passing, making it relatively the hardest to recover.
Elite group players' MTP indicators require an average of 2.64 matches to return to the pre-COVID-19 level, whereas the control group requires 3.55 matches for recovery.The most substantial difference between the two groups is observed in GCA, with the elite group requiring 2.78 matches for recovery, whereas the control group needs 5.64 matches.Our findings indicate that the GCA of control group players before contracting COVID-19 was 0.28, whereas for the elite group, it was 0.47.Referring to the earlier discussion on the significance of GCA in evaluating attacking players, it can be concluded that there is a significant difference between the control group and the elite group, both from the MTP indicator data and the recovery situation.Given that the most important tasks for an attacker are scoring and assisting 79 , this finding illustrates that the greatest advantage of the elite group over the control group lies precisely in this aspect, which also reflects the value of elite group players.
A study on athletes' recovery after contracting COVID-19 indicated that advancing age was linked to a more extended recovery period following COVID-19.Additionally, the prolonged impact of COVID-19 on the recovery to engage in sports seems more protracted in athletes over thirty 91 .Nevertheless, no significant difference is observed based on age when evaluating the number of matches needed for all 100 attacking players to restore their MTP indicators to the pre-COVID level.
When exploring whether age's impact on MTP indicators is moderated by COVID-19 infection, we observed similar results.Regardless of whether players contracted COVID-19, age exerted limited influence on MTP indicators.Specifically, only ShortCmp% exhibited a significant decrease with increasing age after COVID-19 infection.This observation aligns with the conclusions drawn from the separate analysis of the elite group but does not extend to the control group.The aforementioned research conclusion may be related to the fact that all the players in the sample come from the Big Five.The Big Five boasts the world's finest football players and professional management team 68,69 , so in this regard, even the control group's players did not show a significant difference from the elite group's players.
Our study offers a different perspective from Fischer et al.' s research, which observed a more substantial decline in pass performance among players over 30 compared to those under 25 and those between 26 and 30 57 .
It's worth noting that their study focused exclusively on Bundesliga and Serie A players, excluding representation from the Premier League, La Liga, and Ligue 1, potentially limiting the generalizability of their findings to a broader range of elite football players all over the world.Additionally, their inclusion of players from all positions differs from our research, which specifically concentrates on attacking players.Furthermore, the two-season span of their study (2019/2020 and the 2020/2021 seasons) may present challenges in capturing the nuanced impact of age on performance over a more extended period.In contrast, our study aligns with the findings of Rey et al., whose longitudinal study exploring the impacts of aging on match performance in elite football revealed that, despite players with extensive careers struggling to maintain match-related physical performance as they age, they can offset these declines by annually enhancing their technical and tactical skills with increasing age 62 .

Conclusion Recovery and performance insights
This longitudinal study illuminates the match technical performance (MTP) of football attacking players recovering from COVID-19 upon their return to the field.Despite experiencing some negative impact on their MTP after contracting COVID-19, these players demonstrate a relatively swift recovery to their previous level upon resuming matches.Notably, top-level attacking players from the Big Five European Leagues, with their extensive experience and superior overall abilities, exhibit less vulnerability to the negative impact and showcase faster recovery compared to their average-level counterparts.Moreover, age does not significantly impede the MTP of attacking players recovering from COVID-19 upon their return to the field.

Practical implications
Implementing these findings can assist football coaches and managers in developing more targeted recovery training programs for players post-COVID-19 infection or related illnesses.There should be a focus on technical drills aimed at restoring skills that take longer to recover and those most affected in terms of MTP upon returning to play.This study's insights into the impact on MTP and the recovery timeline provide strategic guidance for match preparation, particularly in setting specific tasks and objectives for players in their first few matches back on the field.
This research was exclusively dedicated to attackers within the Big Five.Future studies could extend to include players from various league levels, incorporate more positions, and also cover youth and women's football, broadening the scope and applicability of the findings.

Figure 2 .Figure 3 .
Figure 2. Comparison of significant differences in 28 MTP indicators of 100 attacking players before and after COVID-19 infection (A).

Figure 4 .
Figure 4. Changes in players' MTP indicators over 15 matches before and after COVID-19 infection.In all subplots, the horizontal axis represents the monitored games.The notation − 15 corresponds to the 15th game before COVID-19 infection, while 15 signifies the 15th game after COVID-19 infection, and so forth.The vertical axis of all subplots illustrates the data for various indicators.

Figure 5 .
Figure 5. Average matches needed for players' indicators to recover to pre-COVID-19 levels after infection.

Figure 8 .
Figure 8. Age-related changes in xG, npxG, Touches, and Touches Live before and after COVID-19 infection in the control group.

Table 1 .
92stribution of 100 attacking players in the Big Five European Football Leagues.The association club coefficients are based on the results of each association's clubs in the five previous UEFA Champions League and UEFA Europa League seasons92.If players change the clubs or leagues they play for in the 15 matches before or after contracting COVID-19, we consider the clubs and leagues they are playing for at the time of our statistical analysis.

Table 2 .
Indicators of MTP for attacking players.The mentioned indicators, algorithms, and player data are sourced from FBref and Opta.The primary focus of this study revolves around three pivotal dimensions of MTP concerning attacking players: possession, passing, and shooting 90 .

Table 3 .
Indicators of significant differences in attacking players pre-and post-COVID-19 infection.Differences in MTP indicators between pre-and post-COVID-19 infection are displayed as median differences with 95% confidence intervals.

Table 4 .
Comparison of MTP indicators of the elite and control groups after COVID-19 infection.Differences in MTP indicators between pre-and post-COVID-19 infection are displayed as median differences with 95% confidence intervals.

group Control group Indicators significantly affected after COVID-19 infection in both the elite group and the control group Indicators
Vol:.(1234567890) Scientific Reports | (2024) 14:6057 | https://doi.org/10.1038/s41598-024-56678-ywww.nature.com/scientificreports/ . Notably, only the DriSucc% indicator had a lower average number of matches for the control group (2.54 matches) compared to the elite group (2.66 matches).Overall, the majority of MTP indicators for the elite group players needed fewer matches to return to their pre-COVID-19 levels than the control group, indicating a quicker recovery for the elite group players.Hypothesis 2 was partially validated.